Partial CQI feedback in wireless networks

ABSTRACT

Within a wireless network, feedback information from user equipment (UE) to a control node (eNodeB) is necessary to support various functions. A UE receives an allocation from the eNodeB comprising a plurality of periodic transmission instances for a channel quality indicator (CQI) and a schedule comprising a plurality of periodic transmission instances for a rank indicator (RI), wherein the CQI comprises RI and other CQI fields. The UE then transmits an RI without transmitting the other CQI fields in a transmission instance allocated for both RI and other CQI fields.

CLAIM OF PRIORITY

This application is a continuation of prior application Ser. No.14/682,900, filed Apr. 9, 2015, which is a continuation of priorapplication Ser. No. 12/367,519, filed Feb. 7, 2009, now U.S. Pat. No.9,007,988, which claims priority to U.S. Provisional Application No.61/027,596 entitled “Partial CQI Feedback” filed Feb. 11, 2008, which isincorporated by reference herein. This application for Patent alsoclaims priority to U.S. Provisional Application No. 61/028,023 entitled“Partial CQI Feedback”filed Feb. 12, 2008, which is incorporated byreference herein. This application for Patent also claims priority toU.S. Provisional Application No. 61/029,678 entitled “Partial CQIFeedback ” filed Feb. 19, 2008, which is incorporated by referenceherein,

FIELD OF THE INVENTION

This invention generally relates to wireless communication, and inparticular to providing feedback in orthogonal frequency divisionmultiple access (OFDMA), DFT-spread OFDMA, and single carrier frequencydivision multiple access (SC-FDMA) systems.

BACKGROUND OF THE INVENTION

Wireless cellular communication networks incorporate a number of mobileUEs and a number of NodeBs. A NodeB is generally a fixed station, andmay also be called a base transceiver system (BTS), an access point(AP), a base station (BS), or some other equivalent terminology. Asimprovements of networks are made, the NodeB functionality evolves, so aNodeB is sometimes also referred to as an evolved NodeB (eNodeB or eNB).In general, eNodeB hardware, when deployed, is fixed and stationary,while the UE hardware is portable.

In contrast to eNodeB, the mobile UE can comprise portable hardware.User equipment (UE), also commonly referred to as a terminal or a mobilestation, may be fixed or mobile device and may be a wireless device, acellular phone, a personal digital assistant (PDA), a wireless modemcard, and so on. Uplink communication (UL) refers to a communicationfrom the mobile UE to the eNodeB, whereas downlink (DL) refers tocommunication from the eNodeB to the mobile UE. Each eNodeB containsradio frequency transmitter(s) and the receiver(s) used to communicatedirectly with the mobiles, which move freely around it. Similarly, eachmobile UE contains radio frequency transmitter(s) and the receiver(s)used to communicate directly with the eNodeB. In cellular networks, themobiles cannot communicate directly with each other but have tocommunicate with the eNodeB.

To support dynamic scheduling and multiple-Input multiple-output (MIMO)transmission in downlink (DL), several control information feedback bitsmust be transmitted in uplink. For example, MIMO related feedbackinformation includes: Index of a selected precoding matrix (PMI);transmission rank indicator (RI), which corresponds to the number ofuseful spatial transmission layers; and the recommended/supportablemodulation and coding schemes (MCS). MCS feedback is an index that isassociated with a certain channel coding rate value and modulationscheme (e.g. QPSK, 16QAM, 64QAM). Note that PMI is needed only forclosed-loop spatial multiplexing where channel dependent precoding isemployed. For open-loop spatial multiplexing, only MCS and RI areapplicable.

Control information feedback bits are transmitted, for example, in theuplink (UL), for several purposes. For instance, Downlink HybridAutomatic Repeat ReQuest (HARQ) requires at least one bit of ACK/NACKtransmitted in the uplink, indicating successful or failed cyclicredundancy check(s) (CRC). Moreover, a one bit scheduling requestindicator (SRI) is transmitted in uplink, when UE has new data arrivalfor transmission in uplink. Furthermore, an Indicator of downlinkchannel quality (CQI) needs to be transmitted in the uplink to supportmobile UE scheduling in the downlink. While CQI may be transmitted basedon a periodic or triggered mechanism, the ACK/NACK needs to betransmitted in a timely manner to support the HARQ operation. Note thatACK/NACK is sometimes denoted as ACKNAK, or any other equivalent term.Here, ACK refers to acknowledgement (successful CRC check) and NACKrefers to negative-acknowledgement (failed CRC check). This uplinkcontrol information is typically transmitted using the physical uplinkcontrol channel (PUCCH), as defined by the 3GPP working groups (WG), forevolved universal terrestrial radio access (E-UTRA). The E-UTRA issometimes also referred to as 3GPP long-term evolution (3GPP LTE). Thestructure of the PUCCH is designed to provide sufficiently hightransmission reliability.

In addition to PUCCH, the E-UTRA standard also defines a physical uplinkshared channel (PUSCH), intended for transmission of uplink user data.The Physical Uplink Shared Channel (PUSCH) can be dynamically scheduled.This means that time-frequency resources of PUSCH are re-allocated everysub-frame. This (re)allocation is communicated to the mobile UE usingthe Physical Downlink Control Channel (PDCCH). Alternatively, resourcesof the PUSCH can be allocated semi-statically, via the mechanism ofsemi-persistent scheduling. Thus, any given time-frequency PUSCHresource can possibly be used by any mobile UE, depending on thescheduler allocation. Physical Uplink Control Channel (PUCCH) isdifferent than the PUSCH, and the PUCCH is used for transmission ofuplink control information (UCI). Frequency resources which areallocated for PUCCH are found at the two extreme edges of the uplinkfrequency spectrum. In contrast, frequency resources which are used forPUSCH are in between. Since PUSCH is designed for transmission of userdata, re-transmissions are possible, and PUSCH is expected to begenerally scheduled with less stand-alone sub-frame reliability thanPUCCH. Coded and data bits are multiplexed onto modulation symbols,which are mapped to different resource elements (RE), where an RE isdefined as the smallest granularity of a time-frequency resource. Aresource block (RB) is defined as the aggregation of several REs. Thegeneral operations of the physical channels are described in the E-UTRAspecifications, for example: “3^(rd) Generation Partnership Project;Technical Specification Group Radio Access Network; Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(TS36.211, Release 8).”

The uplink control information is transmitted on PUCCH, if there is noconcurrent transmission of data in the uplink, as defined by 3GPPE-UTRA. In addition, 3GPP E-UTRA defines that in case both uplinkcontrol information and data need to be transmitted in the same uplinksubframe, the uplink control information shall be transmitted on theallocated PUSCH resources, together with data.

A reference signal (RS) is a pre-defined signal, pre-known to bothtransmitter and receiver. The RS can generally be thought of asdeterministic from the perspective of both transmitter and receiver. TheRS is typically transmitted in order for the receiver to estimate thesignal propagation medium. This process is also known as “channelestimation.” Thus, an RS can be transmitted to facilitate channelestimation. Upon deriving channel estimates, these estimates are usedfor demodulation of transmitted information. This type of RS issometimes referred to as De-Modulation RS or DM RS. Note that RS canalso be transmitted for other purposes, such as channel sounding (SRS),synchronization, or any other purpose. Also note that Reference Signal(RS) can be sometimes called the pilot signal, or the training signal,or any other equivalent term.

Turbo codes are a class of high-performance error correction codesdeveloped in 1993 which are finding use in deep space satellitecommunications and other applications where designers seek to achievemaximal information transfer over a limited-bandwidth communication linkin the presence of data-corrupting noise. The channel coding scheme fortransport blocks in LTE is Turbo Coding with a coding rate of R=1/3,using two 8-state constituent encoders and a contention-free quadraticpermutation polynomial (QPP) turbo code internal interleaver. Trellistermination is used for the turbo coding. Before the turbo coding,transport blocks are segmented into byte aligned segments with a maximuminformation block size of 6144 bits. Error detection is supported by theuse of 24 bit CRC. The 1/3 coding rate triples the bit-count fortransmission of the block. The general operations of channel coding aredescribed in the E-UTRA specifications, for example: “3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing andchannel coding (TS36.212, Release 8).” Convolutional codes are also usedin 3GPP E-UTRA for downlink and uplink control channels.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the invention will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIG. 1 is a pictorial of an illustrative telecommunications network thatemploys an embodiment of partial CQI feedback transmission on PUCCH oron PUSCH;

FIG. 2 is an example frame structure for use in transmission betweennodes in the network of FIG. 1;

FIGS. 3A and 3B illustrate placement of reference symbols in the framestructure of FIG. 2 for use in PUCCH;

FIG. 4 is a time plot illustrating periodic Rank and partial MCS/PMIreporting using the structures of FIGS. 3A and 3B;

FIG. 5 is a time plot illustrating partial CQI feedback using thestructures of FIGS. 3A and 3B, where MCS/PMI is dropped in Ranksubframes;

FIG. 6 is a flow diagram illustrating allocation and transmission of RIand MCS/PMI according to an embodiment of the present invention;

FIG. 7 is a block diagram of OFDMA modulation;

FIG. 8 is a block diagram of SC-FDMA modulation; and

FIG. 9 is a block diagram of a Node B and a User Equipment for use inthe network system of FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

MIMO related feedback includes, but is not limited to, the followingfields: Rank Indicator (RI); Modulation and coding scheme (MCS); andprecoding matrix indicator (PMI). Multiple MCS may be required ifspatial multiplexing is employed. Multiple MCS can be expressed in termsof a baseline MCS and a delta MCS relative to the baseline MCS. Withoutloss generality, in this disclosure, CQI may be denoted as the MIMOrelated feedback to its entirety, including but not limited to RI, MCS,and PMI. Alternatively, the term CQI is also used to refer only to MCSfeedback which is differentiated from PMI and RI. In this disclosure, weuse the first definition of CQI although the materials described in thisdisclosure apply regardless of the terminology and the scope for CQI. Wenote again that PMI is applicable only for closed-loop spatialmultiplexing and not for open-loop spatial multiplexing.

In some embodiments of the invention, the CQI feedback can be limiteddue to the limited available resources. An exemplary embodiment is thatif CQI feedback is performed on uplink control channel, e.g. PUCCH in3GPP LTE, there are only 20 coded bits per subframe. If all MIMO relatedfeedback is sent on PUCCH, only limited coding gain for the uplinkcontrol channel is obtained. Thus, it is beneficial to enable partialCQI feedback in order to provide better protection due to a CQI codingrate having a high coding gain.

It is possible that different CQI reports on different time instancescontain different CQI fields, such that multiple CQI reports can becombined to provide a full or more complete CQI reports. In other words,different CQI reports on different time instances can be complimentaryto each other. However, it is not precluded that eNodeB can use each CQIreport alone, even when the CQI report contains partial CQI information,such as not including all CQI fields.

Partial CQI feedback may be enabled to improve CQI detectionperformance. Partial CQI reporting is particularly useful for UEs withcoverage issues, such as cell-edge UEs. It is certainly not precludedthat full CQI reports are employed for cell interior UEs withoutcoverage problem while partial CQI feedback is employed for cell-edgeUEs.

In one embodiment of partial CQI feedback, in the subframes where Rank(RI) and MCS/PMI originally coexist, MCS/PMI is dropped and only Rank(RI) is transmitted, as will be described in more detail below.

FIG. 1 shows an exemplary wireless telecommunications network 100. Theillustrative telecommunications network includes representative basestations 101, 102, and 103; however, a telecommunications networknecessarily includes many more base stations. Each of base stations 101,102, and 103 are operable over corresponding coverage areas 104, 105,and 106. Each base station's coverage area is further divided intocells. In the Illustrated network, each base station's coverage area isdivided into three cells. Handset or other UE 109 is shown in Cell A108, which is within coverage area 104 of base station 101. Base station101 is transmitting to and receiving transmissions from UE 109 viadownlink 110 and uplink 111. As UE 109 moves out of Cell A 108, and intoCell B 107, UE 109 may be handed over to base station 102. Because UE109 is synchronized with base station 101, UE 109 must employnon-synchronized random access to initiate handover to base station 102.A UE in a cell may be stationary such as within a home or office, or maybe moving while a user is walking or riding in a vehicle. UE 109 moveswithin cell 108 with a velocity 112 relative to base station 102.

Cell A 108 allocates a set of resource blocks for UE 109 for its PUSCHtransmission, either by dynamic scheduling or by semi-persistentscheduling. When UE 109 needs to feedback uplink control information inthe same uplink subframe with data, UE 109 transmits both the uplinkcontrol information and data in the allocated PUSCH resource blocks.Similarly, Cell A 108 allocates a resource block for UE 109 for itsPUCCH transmission, either by dynamic scheduling or by semi-persistentscheduling. When UE 109 needs to feedback uplink control informationwithout data, UE 109 transmits the uplink control information in theallocated PUCCH resource block.

As discussed above, channel quality indicator (CQI) needs to be reported(fed back) in uplink (UL) to support dynamic scheduling andmultiple-input-multiple-output (MIMO) transmission on downlink (DL). In3GPP E-UTRA, if a UE (user equipment) has no uplink data transmission,its CQI is transmitted on a dedicated UL control channel (i.e. PUCCH).To support dynamic scheduling and multiple-input multiple-outputtransmission in downlink (DL), several control signaling bits must befed back in uplink (UL). For example, as indicated above, MIMO relatedfeedback information includes: index of a selected precoding matrix(PMI)—applicable only for closed-loop spatial multiplexing; transmissionrank indicator (RI), which is the number of useful spatial transmissionlayers; and supportable modulation and coding schemes (MCS).

RI and the other CQI field(s) (MCS and/or PMI) can be jointly coded andtransmitted in UL. However, since rank information determines the lengthof the CQI information bits and consequently the coding scheme, blinddecoding is necessary for joint coding between RI and the other CQIfield(s) (MCS and/or PMI), which may not provide satisfactoryperformance. In this disclosure, separate RI and MCS/PMI feedbackschemes are described. With separate RI and MCS/PMI transmission, one ormore SC-FDMA symbols can be exclusively dedicated for RI transmission.Furthermore, frequency diversity can be easily achieved by repeating theRI bits on both slots of a subframe. Furthermore, the encoded RI bitsmay be mapped to a certain number of REs or modulation symbols on PUSCH.Since the length of the overall CQI information bits depends on RI, thejoint RI and MCS/PMI transmission scheme may assume the worst (orlongest) CQI length, irrespective of the transmission RI value. WheneverRI is decoded erroneously, CQI is incorrectly received. Moreover, forCQI length shorter than the worst case, some coding gains may be lostsince the longest CQI length is always assumed.

Note the number of CQI information bits is dependent on RI. For widebandMIMO-related feedback in UL, Table 1 shows exemplary numbers of RI andMCS/PMI bits for joint and separate RI and MCS/PMI transmission. Forjoint transmission, to avoid blind decoding at eNodeB, the worst caseCQI length needs to be used, irrespective of the RI value.

TABLE 1 Number of RI and MCS/PMI Bits per Subframe 2-Tx Antennas 4-TxAntennas RI = 1 RI = 2 RI = 1 RI >1 Separate RI 1 RI Bit 1 RI Bit 2 RIBits 2 RI Bits 6 MCS/PMI 8 MCS/PMI 8 MCS/PMI 11 MCS/PMI Bits Bits BitsBits Joint, fixed 9 Bits, RI + MCS/PMI 13 Bits, RI + MCS/PMI (no blinddecoding)

FIG. 2 is an example frame structure 200 for use in transmission betweennodes in the network of FIG. 1. Each frame 200 contains severalsubframes, as indicated generally at 202. In turn, subframe 202 containstwo slots 204, 205. Each slot contains a number of information carryingsymbols, generally indicated at 206. A cyclic prefix (CP) field (notshown) is also appended to each symbol in order to improve receptionintegrity. In the current E-UTRA standard, each slot contains sevensymbols 206 if a normal CP length is used or six symbols 206 if anextended CP length is used. Other embodiments of the invention mayprovide other frame structures than the exemplary frame structureillustrated in FIG. 2.

For PUCCH, a cyclically shifted or phrase ramped CAZAC-like sequence istransmitted in each symbol. Different cyclic shifts or different amountsof phrase ramping can be used to multiplex more than one UEs' PUCCHtransmission in the same physical resource block. A resource block in3GPP E-UTRA is defined as 12 consecutive resource elements in frequencydomain, wherein each resource element is of 15 kHz. Therefore, at most12 CQI UEs can be multiplexed in the same PUCCH resource block. For CQItransmission on PUCCH, with QPSK modulation, 20 coded CQI bits areavailable per UE within one subframe. For ACK/NAK transmission,additional orthogonal covering can be applied across the symbols in thetime domain, thereby increasing the ACK/NAK multiplexing up to 36 UEsper PUCCH resource block. However, due to spillover between consecutivecyclic shifts, it is recommended that not all 12 cyclic shifts areutilized.

In each SC-FDMA symbol, a cyclically shifted or phase ramped CAZAC-likesequence is transmitted. The CAZAC-like sequence in a RS SC-FDMA symbolis un-modulated. The CAZAC-like sequence in a data SC-FDMA symbol ismodulated by the data symbol. Here the data symbol can be the ACK/NAKsymbol, scheduling request indicator (SRI) symbol, Rank Indicator (RI)symbol, or other CQI-related symbol. In this disclosure, a CAZAC-likesequence generally refers to any sequence that has the property ofconstant amplitude zero auto correlation. Examples of CAZAC-likesequences includes but not limited to, Chu Sequences, Frank-ZadoffSequences, Zadoff-Chu (ZC) Sequences, Generalized Chirp-Like (GCL)Sequences, or any computer generated CAZAC sequences. One example of aCAZAC-like sequence r _(u,v)(n) is given byr _(u,v)(n)=e ^(jφ(n)π/4), 0≦n≦M _(sc) ^(RS)−1

where M_(sc) ^(RS)=12 and φ(n) is defined in Table 1.

In this disclosure, the cyclically shifted or phase ramped CAZAC-likesequence is sometimes denoted as cyclic shifted base sequence, cyclicshifted root sequence, phase ramped base sequence, phase ramped rootsequence, or any other equivalent term.

TABLE 2 Definition of φ(n) u φ(0), . . . , φ(11) 0 −1 1 3 −3 3 3 1 1 3 1−3 3 1 1 1 3 3 3 −1 1 −3 −3 1 −3 3 2 1 1 −3 −3 −3 −1 −3 −3 1 −3 1 −1 3−1 1 1 1 1 −1 −3 −3 1 −3 3 −1 4 −1 3 1 −1 1 −1 −3 −1 1 −1 1 3 5 1 −3 3−1 −1 1 1 −1 −1 3 −3 1 6 −1 3 −3 −3 −3 3 1 −1 3 3 −3 1 7 −3 −1 −1 −1 1−3 3 −1 1 −3 3 1 8 1 −3 3 1 −1 −1 −1 1 1 3 −1 1 9 1 −3 −1 3 3 −1 −3 1 11 1 1 10 −1 3 −1 1 1 −3 −3 −1 −3 −3 3 −1 11 3 1 −1 −1 3 3 −3 1 3 1 3 312 1 −3 1 −3 1 1 1 −3 −3 −3 1 1 13 3 3 −3 3 −3 1 1 3 −1 −3 3 3 14 −3 1−1 −3 −1 3 1 3 3 3 −1 1 15 3 −1 1 −3 −1 −1 1 1 3 1 −1 −3 16 1 3 1 −1 1 33 3 −1 −1 3 −1 17 −3 1 1 3 −3 3 −3 −3 3 1 3 −1 18 −3 3 1 1 −3 1 −3 −3 −1−1 1 −3 19 −1 3 1 3 1 −1 −1 3 −3 −1 −3 −1 20 −1 −3 1 1 1 1 3 1 −1 1 −3−1 21 −1 3 −1 1 −3 −3 −3 −3 −3 1 −1 −3 22 1 1 −3 −3 −3 −3 −1 3 −3 1 −3 323 1 1 −1 −3 −1 −3 1 −1 1 3 −1 1 24 1 1 3 1 3 3 −1 1 −1 −3 −3 1 25 1 −33 3 1 3 3 1 −3 −1 −1 3 26 1 3 −3 −3 3 −3 1 −1 −1 3 −1 −3 27 −3 −1 −3 −1−3 3 1 −1 1 3 −3 −3 28 −1 3 −3 3 −1 3 3 −3 3 3 −1 −1 29 3 −3 −3 −1 −1 −3−1 3 −3 3 1 −1

The sequence in different data symbols in FIG. 2 can be different. Inone embodiment, the sequences in different data symbols are cyclicshifted or phase ramped CAZAC-like sequences of a base sequence, withdifferent amounts of cyclic shifts or phase ramps on different datasymbols.

In 3GPP E-UTRA UL, single carrier FDMA (SC-FDMA) is adopted as thetransmission scheme due to its low peak-to-average ratio (PAR) or cubicmetric (CM) property. In the context of CQI transmission on PUCCH,SC-FDMA essentially means a UE can only transmit on one cyclic shift ateach SC-FDMA symbol to keep the PAR/CM low.

The frame structure used in the PUSCH is similar to that illustrated inFIG. 2. Each resource block (RB) in PUSCH contains twelve resourceelements, each of which covers a 15 kHz portion of the frequencyspectrum. However, CDM is not employed in the PUSCH.

FIGS. 3A and 3B illustrate placement of reference signal symbols 310 inthe frame structure of FIG. 2 for use in PUCCH. As discussed above, FIG.3A illustrates a subframe with two slots 304, 305 in the normal CP case.Two reference symbols (RS) 310 are included within each slot. FIG. 3Billustrates a subframe with two slots 304-1, 305-1 in the extended CPcase. In this case, only one reference symbol 310 is included in eachslot. For PUSCH, the structure is similar except that only one RS isused in the normal CP case.

FIG. 4 is a time plot illustrating an example of periodic RI and MCSand/or PMI reporting subframes 402 using the structures of FIGS. 3A and3B on PUCCH, for example. The RI reporting interval 408 can be different(longer) than the MCS/PMI reporting interval 409. Thus, in some MCS/PMIreporting subframes, there is no RI information, such as in subframes408. For the MCS/PMI reporting where RI is included, such as in subframe404, partial CQI reporting may be used. In this case, only partial orrestricted MCS may be transmitted in subframe 404. To further reduce thenumber of CQI bits, PMI may be dropped from each subframe 404 containingRI.

FIG. 5 is a time plot illustrating partial CQI feedback using thestructures of FIGS. 3A and 3B, where MCS/PMI is dropped in RI subframes.In the subframes 504 where RI and MCS/PMI would otherwise coexist,MCS/PMI is dropped and only RI is transmitted.

Still referring to FIG. 5, in subframe 504 where only RI is reported,the RI report can use a designated CQI reporting channel, that is, theUE-specific CQI channel on PUCCH that is allocated by the eNodeB that isserving the cell in which the UE is located. In 3GPP LTE, the CQIchannel on PUCCH consists of 20 coded bits, referred to as PUCCH format2, as described in more detail in 3^(rd) Generation Partnership Project;Technical Specification Group Radio Access Network; Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(referred to as TS36.211, Release 8). Thus, a rate (20, 1) or rate (20,2) coding scheme can be applied to the RI information bits, depending onthe number of RI bits. One such coding is simply a repetition coding.Other coding schemes, such as block coding, are not precluded.

As mentioned above, multiple REs or symbols may be used to transmit RIbits. Denote n as the number of modulation symbols per UL SC-FDMA symbolthat are used for the transmission of coded RI bits. Denote m as thenumber of UL SC-FDMA symbols, within a subframe, that contain coded RImodulation symbols. Therefore, there are a total of (nm) modulationsymbols for the transmission of coded RI bits in a subframe. In 3GPP LTEUL, m can be 4 or 8. Without loss of generality, assuming QPSK(quaternary phase shift keying) as the modulation scheme for thetransmission of coded RI bits, the number of coded RI bits per subframeis 2 nm. Thus, the coding rate (or scheme) for 1 RI bit is (2 nm, 1) andthe coding rate (or scheme) for 2 RI bits is (2 nm, 2). Since the numberof RI bits is either 1 or 2, a simple repetition coding may be used.Table 2 shows an example of the coding scheme for one RI bit with n=3and m=4, while Table 3 shows an example for two RI bits.

TABLE 2 Coding Scheme for 1 RI Bit, n = 3, m = 4 RI Bit Coded RI bits 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1

TABLE 3 Coding Scheme for 2 RI bits, n = 3, m = 4 RI Bit Coded RI bits00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 01 0 1 0 1 0 1 0 1 01 0 1 0 1 0 1 0 1 0 1 0 1 0 1 10 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 01 0 1 0 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Note the value for n can vary for different UEs. For example, for a UEscheduled with high modulation and coding scheme (MCS) for its UL datatransmission, it is presumed that the UE has good channel gain. Thus, itis sufficient for such UE to transmit the coded RI bits on a smallnumber of REs (or modulation symbols) to achieve the required targetperformance. On the other hand, for a UE scheduled with low MCS, it iscommon that this UE does not experience excellent channel condition.Thus, it is crucial for such UE to transmit the coded RI bits on alarger number of REs (or modulation symbols) to achieve the desiredperformance. In the current 3GPP compliant embodiment, the candidatevalues of n can be n=3, 6, 9, or 12. Note the candidate values of m arem=4 or 8. In other embodiments, the range of allowable parameters may bedifferent.

It is not precluded that for simplicity, a fixed value of n and m isadopted to all UEs in the system for the transmission of coded RI bits.Moreover, it is possible to apply a cell-specific or eNodeB specificscrambling code or spreading code to randomize the RI interference fromother cells. A scrambling code or spreading code can be applied to theUL SC-FDMA symbols (possibly including the DM RS SC-FDMA symbol) thatcontain coded RI symbols. The spreading codes can be applied on a slotbasis or on a subframe basis.

It is preferable that the resource or channel used for RI transmissionis the same as the resource or channel for the transmission of other CQIfield(s) (e.g. MCS and/or PMI). For example, in case that RI and MCS/PMIare transmitted separately on uplink control channel, a common PUCCHchannel can be used for the transmission of RI and MCS/PMI, at differenttime instances. One example of such common PUCCH channel is the CQIchannel (PUCCH format 2), defined by a cyclic shift of a CAZAC-likesequence transmitted on a particular physical resource block. It is notprecluded that different resources or channels can be used for separateRI and MCS/PMI transmissions.

When downlink data is received, ACK/NAK must be fed back in uplink. Inthe subframes where RI and ACK/NAK bits coexists in the same subframe,the ACK/NAK bit can be transmitted in the CQI reference signal (RS)symbols, e.g. using PUCCH format 2a, or PUCCH format 2b, as defined inTS 36211, release 8. Refer again to FIG. 3, where RS 310 is illustrated.Alternatively, the RI and ACK/NAK can be jointly coded and transmittedon the (UE-specific) CQI channel. In case RI and ACK/NAK are jointlycoded, the coding scheme will be of rate (20, 1), (20, 2), (20, 3), or(20, 4), depending on the number of RI and ACK/NAK bits. Repetitioncoding or simple block coding scheme (e.g. Reed-Muller codes) can beapplied.

Other embodiments of the proposed partial CQI feedback scheme can beapplied similarly as the example in FIG. 5.

In another embodiment, for the subframes where the proposed partial CQI(including RI) reporting is applied, RI can be multiplexed with otherCQI (e.g. partial MCS or PMI) information field(s) by TDM (time divisionmultiplexing). For example, RI and other (partial) CQI information bitsare separately coded and mapped to different symbols (or OFDM symbols,SC-FDMA symbols) within the reporting subframe.

FIG. 6 is a flow diagram illustrating allocation and transmission of RIand MCS/PMI according to an embodiment of the present invention. Asdescribed above, partial CQI feedback may be used, either for all UEwithin a cell or for UE near an edge of the cell or for UE that areexperiencing interference from various other sources. When a UE enters acell, it receives 602 from the eNodeB serving the cell an allocation ofa set of periodic transmission instances for CQI. It also receives 602an allocation of a set of periodic transmission instances for rankindicator (RI). While RI is part of CQI, as discussed above it may havea different reporting interval that may be longer than the reportinginterval for the other CQI information field(s), such as MCS and PMI. Italso receives configuration information to instruct it as to whichchannel resources it is to use for transmission. In some embodiments, italso receives an indication of a mode of operation to use when RI andthe other CQI information transmissions are both scheduled in the sametransmission instance.

During a normal course of operation, a given UE transmits 620 just thenon-RI CQI feedback information according to its periodic CQIallocation. At the end of each RI interval 604, RI will be transmittedin the allocated transmission instance. In some embodiments, RI will betransmitted 610 without transmitting the other CQI information field(s),such as MCS and PMI. In another embodiment, RI may be transmitted 612with, e.g. partial MCS information, and with partial or no PMIinformation, as discussed in more detail above.

In some embodiments, a control message may have been transmitted 602 tothe UE along with the transmission instance allocation to indicate 606which mode to use when transmitting RI. In this case, in a first mode ofoperation, RI is transmitted 610 without transmitting the other CQIinformation field(s) in the transmission instance. In a second mode ofoperation, both the RI and partial CQI information are transmitted 612in the transmission instance.

Note that this does not preclude the embodiment where RI is alwaystransmitted without transmitting the other CQI field(s) in thetransmission instance. That is, the control message 606 is not present.In this case, MCS and/or PMI are transmitted in instances where RI isnot transmitted.

For embodiments in which a control message indicating a mode ofoperation is not used, then the UE will follow a default procedure. Thedefault may be to transmit 610 an RI without transmitting other CQIfield(s) in a transmission instance allocated for both RI and the otherCQI field(s). Conversely, the default may be to transmit 612 the RIalong with partial other CQI field(s).

The control message indicating a mode of operation may be sent 602 toall user equipment within a cell of the wireless network, or toparticular UE based on interference levels, for example. Thus mode ofoperation may be common to all user equipments within a cell of thewireless network or may be selective.

In some embodiments, the control message 602 further indicates a mode ofoperation in a transmission instance allocated for both ACK/NAK and RI,wherein in one mode ACK/NAK is transmitted by modulating a referencesignal (RS) of the transmission instance. In another mode, ACKNAK and RIare jointly coded, as described in more detail above.

In various embodiments, CQI feedback is accomplished using one of thestructures described in more detail in FIGS. 7 and 8, where atransmission instance comprises of a plurality of SC-FDMA symbols.

FIG. 7 is a block diagram of an illustrative orthogonalfrequency-division multiplexing (OFDM) system transmitter 700 fortransmitting the frame structures of FIG. 2. Elements of the transmittermay be implemented as components in a fixed or programmable processor byexecuting instructions stored in memory, for example, or by dedicatedcircuitry, for example. The UE generates a CAZAC-like (e.g. ZC orextended ZC or zero-autocorrelation QPSK computer-generated) sequenceusing base sequence generator 702. One embodiment of the CAZAC-likesignal from generator 702 in FIG. 7 is a cyclically shifted or phaseramped CAZAC-like sequence, as described above in more detail withrespect to Table 1. A cyclic shift value is selected for each symbolbased on the resource index, the SC-FDMA symbol number and the slotnumber in cyclic shift selecting module 704. The base sequence is thenshifted by cyclic shifter 706 on a symbol by symbol basis using shiftvalues provided by cyclic shift selection module 704.

The separate RI and the other feedback data per SC-FDMA symbol isorganized as either one or two bits in this embodiment and is input tomodulator block 720. The data bearing SC-FDMA symbols are binary phaseshift key (BPSK) or quadrature phase shift key (QPSK) modulated when thedata information is one or two bits wide, respectively. The switch 726selects, based on the SC-FDMA symbol type (data or RS), either thecomplex BPSK/QPSK constellation point or “1” as input to the complexmultiplier 724.

The result of the element-wise complex multiplication is mapped onto adesignated set of tones (sub-carriers) using the Tone Map 730. The UEnext performs IFFT of the mapped signal using the IFFT 732. A cyclicprefix is created and added in module 734 to form a final fully formeduplink signal 736.

FIG. 8 illustrates an alternate modulation block 852 to that of FIG. 7.Block [c_(k)(0) . . . c_(k)(L−1)] 850 denotes the user signal of user kthat includes separate RI and other CQI field feedback as describedabove. This user signal includes but is not limited to reference signal,data signal and control signal. Modulation block 852 includes discreteFourier Transform (DFT) block 856, tone map 853, inverse Fast Fouriertransform (IFFT) block 854 and parallel-to-serial (P/S) converter 855.In FIG. 8, the user signal is first processed by DFT block 856. Tone map853 maps the user signal onto L sub-carriers as described above inconjunction with FIG. 7. IFFT block 854 converts these signals fromfrequency domain to temporal domain. Copies of modulation block 852 inFIG. 8 can service a plurality of UEs. The plural of signals from theplural UEs are transmitted on different sub-carriers at the same timeperiod as designated by a UE specific tone map 853. Such a system issometimes called single carrier orthogonal frequency division multipleaccess (SC-FDMA) system. These plural user signals, DFT blocks and tonemaps are omitted for clarity. P/S converter 856 converts these parallelsignals into a single serial signal 860. A cyclic prefix (CP) 861 isinserted by repeating a portion of the serial signal.

FIG. 9 is a block diagram illustrating operation of a eNodeB 902 and amobile UE 901 in the network system of FIG. 1. The mobile UE device 901may represent any of a variety of devices such as a server, a desktopcomputer, a laptop computer, a cellular phone, a Personal DigitalAssistant (PDA), a smart phone or other electronic devices. In someembodiments, the electronic mobile UE device 901 communicates with theeNodeB 902 based on a LTE or E-UTRAN protocol. Alternatively, anothercommunication protocol now known or later developed can be used.

As shown, the mobile UE device 901 comprises a processor 910 coupled toa memory 912 and a Transceiver 920. The memory 912 stores (software)applications 914 for execution by the processor 910. The applicationscould comprise any known or future application useful for individuals ororganizations. As an example, such applications could be categorized asoperating systems (OS), device drivers, databases, multimedia tools,presentation tools, Internet browsers, e-mailers, Voice-Over-InternetProtocol (VOIP) tools, file browsers, firewalls, instant messaging,finance tools, games, word processors or other categories. Regardless ofthe exact nature of the applications, at least some of the applicationsmay direct the mobile UE device 901 to transmit UL signals to the eNodeB(base-station) 902 periodically or continuously via the transceiver 920.In at least some embodiments, the mobile UE device 901 identifies aQuality of Service (QoS) requirement when requesting an uplink resourcefrom the eNodeB 902. In some cases, the QoS requirement may beimplicitly derived by the eNodeB 902 from the type of traffic supportedby the mobile UE device 901. As an example, VOIP and gaming applicationsoften involve low-latency uplink (UL) transmissions while HighThroughput (HTP)/Hypertext Transmission Protocol (HTTP) traffic caninvolve high-latency uplink transmissions.

Transceiver 920 includes uplink logic which may be implemented byexecution of instructions that control the operation of the transceiver.Some of these instructions may be stored in memory 912 and executed whenneeded by processor 910. As would be understood by one of skill in theart, the components of the Uplink Logic may involve the physical (PHY)layer and/or the Media Access Control (MAC) layer of the transceiver920. Transceiver 920 includes one or more receivers 922 and one or moretransmitters 924.

Processor 910 may send or receive data to various input/output devices926. A subscriber identity module (SIM) card stores and retrievesinformation used for making calls via the cellular system. A Bluetoothbaseband unit may be provided for wireless connection to a microphoneand headset for sending and receiving voice data. Processor 910 may sendinformation to a display unit for interaction with a user of the mobileUE during a call process. The display may also display pictures receivedfrom the network, from a local camera, or from other sources such as aUSB connector. Processor 910 may also send a video stream to the displaythat is received from various sources such as the cellular network viaRF transceiver 922 or the camera. It should be understood that UE 901may contain more than one processor and that processor 910 is thereforerepresentative of processing circuitry that may be embodied to performthe functions described herein.

During transmission and reception of voice data or other applicationdata, transmitter 924 sends ACKNAK information and CQI feedbackinformation via the PUCCH and/or the PUSCH links to the serving eNodeB902, as described in more detail above. In particular, RI feedback isscheduled with a longer reporting interval than the other CQIinformation field(s). Rank indicator (RI) is transmitted on itsscheduled reporting interval without transmitting the other CQIinformation field(s) in a transmission instance allocated for both RIand other CQI information field(s).

In this embodiment, control of the partial CQI feedback transmission isembodied by executing instructions stored in memory 912 by processor910. In other embodiments, the scheme may be embodied by a separateprocessor/memory unit, by a hardwired state machine, or by other typesof control logic, for example.

The CQI feedback subframes are then transmitted by transmitter 924, asdescribed in more detail with regard to FIGS. 7-8.

NodeB 902 comprises a Processor 930 coupled to a memory 932, symbolprocessing circuitry 938, and a transceiver 940 via backplane bus 936.The memory stores applications 934 for execution by processor 930. Theapplications could comprise any known or future application useful formanaging wireless communications. At least some of the applications 934may direct the base-station to manage transmissions to or from the userdevice 901.

Transceiver 940 comprises an uplink Resource Manager, which enables theeNodeB 902 to selectively allocate uplink PUSCH resources to the userdevice 901. As would be understood by one of skill in the art, thecomponents of the uplink resource manager may involve the physical (PHY)layer and/or the Media Access Control (MAC) layer of the transceiver940. Transceiver 940 includes one or more receiver(s) 942 for receivingtransmissions from various UE within range of the eNodeB andtransmitter(s) 944 for transmitting data and control information to thevarious UE within range of the eNodeB.

The uplink resource manager executes instructions that control theoperation of transceiver 940. Some of these instructions may be locatedin memory 932 and executed when needed on processor 930. The resourcemanager controls the transmission resources allocated to each UE that isbeing served by eNodeB 902 and broadcasts control information via thephysical downlink control channel PDCCH.

Symbol processing circuitry 938 performs demodulation and reverse ratematching using known techniques. CQI feedback is received via receiver942 via PUCCH or PUSCH from a particular UE that has provided partialCQI feedback, as described in more detail above. eNodeB 902 may combineseveral partial CQI feedback transmissions to determine a complete CQIstatus for a given UE. It is possible that different CQI reports ondifferent time instances contain different CQI field(s), such thatmultiple CQI reports can be combined to provide a full or more completedCQI reports. In other words, different CQI reports on different timeinstances can be complimentary to each other. However, it is notprecluded that eNodeB can use each CQI report alone, even when the CQIreport contains partial CQI information, such as not including all CQIfields.

Other Embodiments

Various other embodiments of the invention will be apparent to personsskilled in the art upon reference to this description. For example, alarger or smaller number of symbols then described herein may be used ina slot. Other types of feedback may be separately embedded andtransmitted in configured frames at various times. The term “frame”,“subframe” and “slot” are not restricted to the structure of FIG. 2.Other configurations of frames and/or subframes may be embodied. Ingeneral, the term “frame” may refer to a set of one or more subframes. Atransmission instance likewise refers to a frame, subframe, or otheragreed upon quantity of transmission resource in which a feedbackindication can be embedded.

While the disclosure has discussed a scheme for the transmission offeedback information with data on PUCCH that provides for partial CQIfeedback capability, other embodiments may use the principles describedherein to improve reliability for signaling other types of informationthat is routinely signaled between nodes in a network that have anaspect of dynamic variability in accuracy based on channel conditions.

Some embodiments of partial CQI feedback include, but are not limited tothe following examples.

-   -   Only RI is reported.    -   Only MCS is reported, which may be the baseline MCS, the delta        MCS, or both. A eNodeB or the UE transmitter can assume or use        the RI and/or PMI which was fed back earlier. Alternatively, the        eNodeB or transmitter can assume fixed RI and/or PMI.    -   Only PMI is reported. The eNodeB or UE transmitter can assume or        use the RI and/or MCS which was fed back earlier. Alternatively,        the eNodeB or transmitter can assume fixed RI and/or MCS.    -   MCS and PMI are reported, without RI. The eNodeB or UE        transmitter can assume or use the RI which was reported (fed        back) earlier. Alternatively, the eNodeB or transmitter can        assume a fixed RI.    -   RI and MCS is reported, without PMI. The eNodeB or UE        transmitter can assume or use the RI which was fed back earlier.        Alternatively, the eNodeB or transmitter can assume a fixed PMI.    -   RI and PMI only are reported.    -   Sending CQI information with coarse frequency granularity to        reduce the number of CQI reporting bits    -   Sending RI and partial or restricted MCS information, with or        without PMI        -   a. Restrict the allowed MCS for MIMO transmission. Thus,            fewer MCS bits need to be reported on CQI feedback. This            restriction (possibly different restriction rules) applies            to both the baseline MCS or the delta MCS.        -   b. In case of spatial multiplexing with 2 codewords, only            sends the baseline MCS. It is possible to send the delta MCS            and/or baseline MCS in future CQI feedback, where RI may not            be transmitted (or fed back)        -   c. Restricting the usage of spatial multiplexing of 2 or            more codewords, such that only 1 MCS is fed back    -   Sending RI and partial or restricted PMI information, with or        without full/partial MCS information; for example, by        restricting the allowed precoding matrices, which reduces the        number of PMI feedback bits.

It is not precluded that the proposed partial CQI feedback scheme isalso implemented when CQI is fed back in data channel, e.g. PUSCH in3GPP LTE.

As used herein, the terms “applied,” “coupled,” “connected,” and“connection” mean electrically connected, including where additionalelements may be in the electrical connection path. “Associated” means acontrolling relationship, such as a memory resource that is controlledby an associated port. While the Invention has been described withreference to illustrative embodiments, this description is not intendedto be construed in a limiting sense.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the invention.

The invention claimed is:
 1. An apparatus, comprising: circuitry fortransmitting an allocation comprising a plurality of periodictransmission instances for a channel quality indicator (CQI), whereinthe CQI comprises a rank indicator (RI) and at least one other CQIfield; circuitry for transmitting a schedule comprising a plurality ofperiodic transmission instances for the RI; and circuitry for receivinga first RI without receiving the other CQI fields in a firsttransmission instance of the plurality of periodic transmissioninstances allocated for both RI and other CQI fields.
 2. The apparatusof claim 1, wherein the other CQI fields comprise a modulation andcoding scheme (MCS) index associated with a channel coding rate valueand modulation scheme, and a precoding matrix indicator (PMI).
 3. Theapparatus of claim 1, wherein the other CQI fields comprise only amodulation and coding scheme (MCS) index associated with a channelcoding rate value and modulation scheme.
 4. The apparatus of claim 1,further comprising circuitry for transmitting a control messageindicating a mode of operation in a transmission instance allocated forboth the RI and the other CQI fields, wherein in a first mode ofoperation, the first RI is received without receiving the other CQIfields in the first transmission instance; wherein in a second mode ofoperation, both the first RI and a portion of the other CQI fields arereceived in the first transmission instance.
 5. The apparatus of claim4, wherein a receiving instance comprises a plurality of single carrierorthogonal frequency division multiple access (SC-FDMA) symbols andfurthermore, at least one SC-FDMA symbol is used for receiving the RIand at least another SC-FDMA symbol is used for the transmission of theother CQI fields.
 6. The apparatus of claim 1, wherein a same channelresource is used for the receiving of both the RI and the other CQIfields.
 7. The apparatus of claim 6, wherein the channel resourcecorresponds to a selected cyclic shift of a designated sequence within agiven physical resource block.
 8. The apparatus of claim 1, wherein anACKNAK is received in the same receiving instance as the RI, wherein theACK/NAK is received by demodulating a reference signal (RS) of thereceiving instance.
 9. Apparatus for use in a wireless network,comprising: circuitry for transmitting a resource allocation comprisinga plurality of periodic transmission instances for channel qualityindicator (CQI) feedback and a schedule comprising a plurality ofperiodic transmission instances for rank indicator (RI) feedback,wherein the CQI comprises RI and at least one other CQI fields; andcircuitry for receiving a first RI without the other CQI fields in afirst transmission instance allocated for both RI and other CQI fields.10. The apparatus of claim 9, wherein the other CQI fields comprise amodulation and coding scheme (MCS) index associated with a channelcoding rate value and modulation scheme, and a precoding matrixindicator (PMI).
 11. The apparatus of claim 9, wherein the other CQIfields comprise only a modulation and coding scheme (MCS) indexassociated with a channel coding rate value and modulation scheme. 12.The apparatus of claim 9, wherein the circuitry for transmitting isfurther operable to generate and transmit a control message indicating amode of operation in a receiving instance allocated for both RI andother CQI fields; and wherein in a first mode of operation, thecircuitry for receiving is operable to receive the first RI withoutreceiving the other CQI fields in the first receiving instance, and in asecond mode of operation, the circuitry for receiving is operable toreceive both the first RI and a portion of the other CQI fields in thefirst receiving instance.
 13. The apparatus of claim 12, wherein atransmission instance comprises a plurality of single carrier orthogonalfrequency division multiple access (SC-FDMA) symbols and furthermore, atleast one SC-FDMA symbol is used for the transmission of RI and at leastanother SC-FDMA symbol is used for the transmission of the other CQIfields.
 14. The apparatus of claim 9, wherein a same channel resource isused for receiving both the RI and the other COI fields, wherein thechannel resource corresponds to a selected cyclic shift of a designatedsequence within a given physical resource block.
 15. The apparatus ofclaim 9, wherein the circuitry for receiving is operable to receive anACKNAK in the same receiving instance as the RI, wherein the ACK/NAK isreceived by demodulating a reference signal (RS) of the receivinginstance.
 16. An apparatus, comprising: means for transmitting to a userequipment in the network an allocation comprising a plurality ofperiodic transmission instances for a channel quality indicator (CQI),wherein the CQI comprises a rank indicator (RI) and at least one otherCQI field; means for transmitting to the user equipment a RI reportinginterval comprising a plurality of periodic transmission instances forthe RI; and means for receiving from the user equipment a first RIwithout receiving the other CQI fields in one of the plurality ofperiodic transmission instances allocated for both RI and other CQIfields.
 17. The apparatus of claim 16, wherein the other CQI fieldscomprise a modulation and coding scheme (MCS) index associated with achannel coding rate value and modulation scheme, and a preceding matrixindicator (PMI).
 18. The apparatus of claim 16, wherein the other CQIfields comprise only a modulation and coding scheme (MCS) indexassociated with a channel coding rate value and modulation scheme. 19.The apparatus of claim 16, further comprising circuitry for transmittingto the user equipment a control message indicating a mode of operationin a transmission instance allocated for both RI and other CQI fields,wherein in a first mode of operation, a first RI is received withoutreceiving the other CQI fields in a first transmission instance; whereinin a second mode of operation, both the first RI and a portion of theother CQI fields are received in the first transmission instance. 20.The apparatus of claim 19, wherein a transmission instance comprises aplurality of single carrier orthogonal frequency division multipleaccess (SC-FDMA) symbols and furthermore, at least one SC-FDMA symbol isused for the transmission of the RI and at least another SC-FDMA symbolis used for the transmission of the other CQI fields.
 21. The apparatusof claim 16, wherein both the RI and the other CQI fields are receivedon a same channel resource.
 22. The apparatus of claim 21, wherein thechannel resource corresponds to a selected cyclic shift of a designatedsequence within a given physical resource block.
 23. The apparatus ofclaim 16, wherein an ACKNAK is received from the user equipment in thesame transmission instance as the first RI, wherein the ACK/NAK isdetermined by demodulating a reference signal (RS) of the sametransmission instance.